1. Field of the Invention
The present invention relates generally to a hybrid Local Area Network (LAN) for interconnecting multiple stations, and more particularly pertains to a LAN in which a non-blocking any-to-any switch interconnects one or more passive star subnetworks, with the LAN providing for any-to-any interconnections, multiple simultaneous transmissions, or broadcasting.
2. Discussion of the Prior Art LANs based on passive optical coupler technology provide a low-cost, high-reliability communications mechanism for interconnecting distributed systems. A potential limitation of this technology, however, is the fan-out limitations of passive optical couplers. Light that enters into an n-input by n-output coupler is split n-ways, effectively being reduced in intensity by a factor of n. The allowable optical power budget between the network transmitters and receivers, for an acceptable bit-error rate operation, determines the maximum size of the network. Under current technological capabilities, for the case of semiconductor type laser transmitters, networks of size 32 stations, and perhaps 64 stations, are possible.
In a distributed computing environment, however, a larger number of stations may require interconnection. In large networks, i.e. with &gt;64 attached stations, the fanout limitations of the optical coupler must be addressed. In addition, the performance characteristics of the network may be degraded because of the shared medium nature of the coupler mechanism that allows only one data transmission to take place at any given time.
In order to solve the above problems, multiple coupler subnetworks may be used, wherein each subnetwork services a subset of the given stations. To allow communication between the subnetworks, a coupling mechanism must be used. In the prior art, the coupling of two LANs is often accomplished via a station, called a bridge, that has interfaces to both LANs, and buffers for storing the messages that are to be transmitted from one LAN to the other. The bridge must have sufficient processing power to handle the protocol of both LANs. The size of the bridge buffers typically depends on message size and the particular protocol used on the LANs. Bridges tend to introduce delays in the store-and-forwarding of messages between LANs, and the additional processing and buffer requirements for handling the message transfer function make them costly.
Some prior art LANs provide for the transmission of data between a plurality of nodes by a technique known as store-and-forwarding, which means that the entire package is stored in an intermediate network node before it is passed on to the next node. The node could be a switch or could be a processor. Store-and-forwarding increases the complexity of the system because packet buffers must be managed, along with pacing control, tracking and recovery of lost packets, etc.
A copending U.S. patent application, Ser. No. 07/429,267 filed on Oct. 30, 1989, by the same assignee as the current application, discloses the use of delimiters to control physical crosspoint connections.